Ligand Engineering Enables Fast Kinetics of KVPO4F Cathode for Potassium-Ion Batteries

Vanadium-based fluoride phosphate polyanionic compounds are the most competitive candidates for cathode materials in potassium-ion batteries (PIBs). However, they have faced the long-standing obstacle of poor intrinsic kinetics that has yet to be overcome, ascribed to the unique electron transfer pattern in the covalently bonded structures. Herein, by adjusting the coordinated circumstance of the V octahedron via the introduction of a large-sized and weak-field ligand Cl^–, we synthesized KVPO₄F_0.9Cl_0.1 (KVPFCl) with fast kinetics. A distorted octahedral symmetry with the larger Cl^– expands the lattice structure, facilitating K⁺ ion diffusion in the KVPFCl material. Furthermore, accelerated electronic kinetics is achieved via the stronger electron donor Cl^–, which stimulates the hybridization of the V 3d orbital and the 2p/3p orbitals of the ligands and narrows the crystal field splitting energy. Therefore, the as-prepared KVPFCl has a high rate capability and capacity retention. Our results provide prospective insights into achieving fast kinetics in vanadium fluorophosphate polyanionic materials for PIBs.